The Modification of Developmental Patterns in the Sand Dollar by Sodium Selenite

Abstract

E :PERIMENTS dealing with the modification of developmental pattern in the echinoderm egg by external agents are not new. Sixty years ago Herbst (1892) discovered that lithium would cause exogastrulation and vegetalization in the developing larva of the sea urchin. Child (1941a, pp. 197-246) reviewed the various agents that affect development differentially and pointed out that differential inhibition, differential recovery, and differential conditioning in a quantitatively graded physiological system may be largely responsible for modifications in development caused by external agents. Recently, others (Hbrstadius and Gustafson, 1947; see Hirstadius, 1949, for review) have found that certain substances (propanediol phosphate, phosphogluconic acid, lactate), which are thought to play a role in carbohydrate metabolism, cause an animalization in apical halves of the sea-urchin egg, while other substances (certain amino acids), which may tend to favor protein metabolism, cause vegetalization. Also recently, the author (Rulon, 1949; 1950a, b; 1951) has shown that in the developing egg of the sand dollar (Dendraster excentricus) certain enzyme inhibitors (azide, thiourea) promote vegetalization, while others (maleic acid, malonic acid) promote overdevelopment of the animal region. The different inhibitors also have other dissimilar effects. In continuation of this work and in an effort to learn more con-